python3 distutils reports path which is not in sys.path for /usr/local prefix

[Tobias Faller]

sysconfig.distutils.get_python_lib() reports the path '/usr/local/lib/python3/dist-packages' for the prefix '/usr/local'.
This does not match the path '/usr/local/lib/python3.6/dist-packages' which is listed in sys.path.

Command: python3 -c "from distutils import sysconfig; print(sysconfig.get_python_lib(prefix='/usr/local'))"
Output: /usr/local/lib/python3/dist-packages

Command: python3 -c "import sys; print(sys.path)"
Output: ['', '/usr/local/python36.zip', '/usr/lib/python3.6', '/usr/lib/python3.6/lib-dynload', '/home/administrator/.local/lib/python3.6/site-packages', '/usr/local/lib/python3.6/dist-packages', '/usr/lib/python3/dist-packages']

Ubuntu release version: Ubuntu 18.04.3 LTS
python3-distutils version: 3.6.8~18.04

If this is a bug then this could be fixed by patching distutils/sysconfig.py in some way. (attached)